1. Field of the Invention
This invention relates to an interconnecting power generation system and, more particularly, to an interconnecting power generation system for supplying electrical power to an interconnecting load in conjunction with a utility power system.
2. Description of the Related Art
In general, an interconnecting power generation system comprises an inverter apparatus for converting a DC output of a solar power generation system for example as a DC power source into an AC output and linking the DC power source to an AC utility power supply. A control unit for controlling the inverter apparatus has a detection circuit for detecting the phase voltage of the utility power supply, a detection circuit for detecting the output current of the inverter apparatus, an arithmetic circuit for calculating the error between signals indicating the phase voltage of the utility power supply and the output current of the inverter apparatus detected by the respective detection circuits, and a driver circuit for controlling the switching of the inverter apparatus based on the output of the arithmetic circuit, and makes the output current outputted from the current-controlled inverter apparatus follow the phase voltage signal of the utility power supply so that a sine wave current coincident in phase with the voltage of the utility power supply can be outputted. The interconnecting power generation system thereby converts electrical power generated by a solar cell into AC electrical power for example.
However, in order to interrupt power supply in a utility power system intentionally for maintenance or inspection, a switch upstream of the power outage section must be opened to interrupt the power supply to the section. When an interconnecting power generation system described as above is installed in or connected to the power outage section, it is necessary to detect the power outage and open a switch interposed between the interconnecting power generation system and the utility power system to isolate the interconnecting power generation system from the utility power system.
When an abnormality in the utility power supply such as an over-frequency or under-frequency condition is detected, the interconnecting power generation system must be isolated from the utility power system by opening the switch.
Moreover, in an interconnecting power generation system comprising a turbogenerator, at the moment when the interconnecting power generation system is isolated from the utility power system, the generator is put into a no-load operating condition to the rotational speed of the turbine rapidly increase to exceed the absolute rated speed, resulting in damage to the turbine or the auxiliaries.
The present invention has been made in view of the above circumstances and it is, therefore, an object of the present invention to provide an interconnecting power generation system which can detect an abnormality in the utility power supply and can be isolated from the utility power system and can prevent damage to a turbogenerator.